Transportation Electrification: Opportunities and Challenges

By: Babak Fahimi, PhD

University of Texas at DallasRenewable Energy and Vehicular Technology Laboratory

Tel: 972-883-6609EML: fahimi@utdallas.edu

University of Texas at Dallas

Organization

•Introduction.

• Challenges.

• Electrification methodologies.

• Opportunities.

• Conclusions.

Introduction

Introduction

Introduction

Observations

Introduction

Introduction

Introduction

Emissions of Greenhouse GasesCO2, CH4, and N2OVOC, CO, and NOx as optional GHGs

Emissions of Five Criteria Pollutants (Total and Urban Separately)

VOC, CO, NOx, PM10, and SOx

Energy UseAll energy sources Fossil fuelsPetroleum

Introduction

Introduction

Introduction

Introduction

• Energy: efficient, Alternative Fuels.• Environment: Minimal Emissions.• Safety and Intelligent.

• Power train: Electrification and hybridization.•Control: New Control theory and algorithm, Computerization and digitalization.

• Future Vehicles: 4 Wheels+ Computers.

Energy stored in one gal. of gasoline: 130MJ or 36 kWh.

Energy density: 12.9 kWh/kg( about 100 times of Li-ion battery)

Time to fill up a 31 gal tank (Suburban): 211 sec.

Average rate of energy transfer: 19MW

This is the competition for battery/battery chargers!

Challenges

How about Fuel Cell car?

0 10 20 30 40 50 60 70 80 900

0.1

0.2

0.3

0.4

0.5

0.6

0.7

Gamma

Ove

rall

Effi

cien

cy

nfc = 20%nfc = 40%nfc = 60%nfc = 80%nfc = 100%

Economically feasible?

Challenges

How about Fuel Cell car?

Fuel Cell efficiencies are way to low to make a sound economical case!

+ KJ8.484

Challenges

Key technologies missing:

1. High efficiency thermoelectric energy converters!

2. High energy density+ High power density energy storage elements!

3. Faster Photosynthesis !

4. High efficiency fuel cells!

Challenges

Electrification Methodologies

Alternatives

Electrification Methodologies

Pre-transmissionParallel (belt driven, crankshaft mounted, or integrated with torque converter)Series/parallel switching (single motor with dual clutches)Power split (dual M/G and no clutches, e.g., “electric-CVT”)

Post-transmissionTransfer case mountedAxle mounted or in differential case (ie part of the final drive)Wheel motor

SeriesMotor generator set or fuel cell to dc link (direct or via converter)Can be electric peaking (w/battery) or load following configuration (ie, locomotive drive)

E4 (electric four wheel drive)Autonomous (engine driven alternator to axle M/G – Hitachi system)Hybridized E4 (part of HV driveline)

Types of HEV

Electrification Methodologies

Parallel, pre-transmission: Integrated Starter AlternatorISA/ISG/CSA/FWA/IMA5%<EF<15%

Powersplit with either epicyclic or continuously variable transmission10%<EF<50%

e-mtr

PowerInverter

EnergyStorage

Trans & FD

EnergyStorage

PowerInverter

PowerInverter

M/G1

M/G2

Electrification Methodologies

Brief introduction to epicyclic based power split architectureIn the power split architecture dual M/G’s and a epicyclic gear set act as a CVT and maintain the engine speed variations relatively small.

R

C

S

M/G

ICE

S/A

Gearbox FD

wheels

Electrification Methodologies

Electric four wheel drive.Generally in combination with a pre-transmission hybrid.10 kW<PE4<25 kW

Series hybrid electric.Presently economical on commercial trucks and city buses. Weight & complexityBasis for FCHVSmall battery load trackingLarge battery electric peaking

PowerInverter

EnergyStorage

Alt

e-mtr

Gear

EnergyStorage

PowerInverter

PowerRectifier

Gen e-mtr

Electrification Methodologies

Series-parallel switchingCVT, MT, or AT capableToyota has in production on city bus

Fuel Cell HVEnergy storage system with interface converter. This arch is applicable to battery and ultra-capacitor storage systems.Same arch for stationary powerConverter inhibits back driving fuel cell

e-mtr PowerInverter

EnergyStorage

CVT Trans & FD

Flywheel

C1

C2

C3

SupervisoryControl

FuelTank

Fuel Pump

Ref

orm

er

Induction Air

Radiator

AirCompressor

Humidifier

CoolantPump

FC Stack Cooling Loop

Exhaust& VaporRecovery

De-ionized water

EMI common mode& transverse modefilter bank if utilityinterconnection Traction

Motor ORUtility

EnergyStorageSystem

Exhaust

Fuel Cell Stack

dc/dc Booster

dc/ac converter

Electrification Methodologies

Fuel cell power plants in mobile applications are fully series hybrid.

Electric peaking if fuel cell is rated for average load and on board battery is capable of electric only range.Load tracking if battery is minimal or not used. Ultra-capacitor used for regenenergy recovery. Fuel cell plant must have faster dynamics. Toyota has precursor to this in ES3 concept HV with ultra-capacitor energy storage system.

FuelTank

Fuel Pump

Ref

orm

er

Induction Air

Radiator

AirCompressor

Humidifier

CoolantPump

FC Stack Cooling Loop

Exhaust& VaporRecovery

De-ionized water

EMI common mode& transverse modefilter bank if utilityinterconnection Traction

Motor ORUtility

EnergyStorageSystem

Exhaust

Fuel Cell Stack

dc/dc Booster

dc/ac converter

Electrification Methodologies

Hybrid vehicle technology already offers benefits in fuel economy and low emissions but lack performanceThe new generation of hybrid drivelines delivers V8 performance with a V6 and a up-rated electric drive operating at ~600Vdc.More compact power electronics. More efficient M/G.EMI issues at high dV/dt?Electrical safety if 600V?

Lexus RX 330

Electrification Methodologies

The S2000 Roadster with a cruising range of >650 miles at an average fuel economy of 51mpg.Room for 5 and performance from a 1.3 liter gasoline engine that has its low end torque boosted 66% by a 144V synchronous permanent magnet motor/generator (M/G) rated 10 kW at 4000 rpm.Ac drive system operates in constant torque over most of the engine torque-speed range.

Electrification Methodologies

144V NiMH battery10 kW (13.4 Hp) PM Direct parallel config.

Electrification Methodologies

Hybrid Sport Utility Vehicle, Hybrid Escape announced at the 2000 LA Auto Show. Slated for mass production later in 2003. Delivers 40 mpg (city) and meets SULEV emissions300V powersplitarchitecture, NiMH battery, 65 kW M/G and 28 kW S/A deliver same performance as 200 Hp V6

Electrification Methodologies

2003 introduction of Silverado & Sierra 42V ISG pickups2006 hybrid SUV the Chevy Equinox with CVT transmission2007 mass production of hybrid Chevy Malibu2007 hybrid full size SUV’s the Tahoe and YukonConcept vehicles:GM autonomyGM Hywire

fully Digital networkedFlexray, TTP/C, or CAN?OEM Consortium in progress.

Electrification Methodologies

Low voltage, mild hybrid. 42V belt ISA14V Belt ISA is popular in Europe

High voltage, full hybrid. GM Paradigm system (power split)Capable of operating accessories by electric drive with engine off and vehicle parked.

Electrification Methodologies

Toyota Estima minivan with pre-transmission, powersplit hybrid front axle drive and electric rear axle drive.Energy storage system in rear. Electronic power processing in front. EMI concerns?

Opportunities

Engine for Energy (range)

Battery for Energy (range)Capacitor Power

Electric Motor for Power

Opportunities•Performance, Economy and Reliability:

•Stable and consistent performance at all temperatures.• Improved gas mileage in cold weather.• Longer battery life.

Prediction is for 1M PHEV & BEV globally in 2015 growing to 4M in 2020

Opportunities• The 5 key assertions about ultracapacitor-battery combination

• Improved reliability and life for cold temperature performance,• Full energy capture during regeneration at top of battery charge,• Full power delivery capability at end of life without battery oversizing,• Enables use of higher specific energy battery with lower cost and power,• Higher overall efficiency. Battery losses are moved out and minimized in

the ultracapacitor. (excerpted from Ted Bohn, Argonne Labs).

Precedents of ultracapacitor-battery combinationsConsumer

Ultracaps~32V / 70F

12 VBattery

DC DC

G

<2000W

14V

Audi recuperator systemFor reduced fuel consumption

Ultracapacitor

DC

12V Battery

12 V BordnetStarter-alternatorReversible system

Control unit

High powerelectrical loads

DC

Ultracapacitor

DC

12V Battery

12 V BordnetStarter-alternatorReversible system

Control unit

High powerelectrical loads

DC

Valeo reversible alternator system with combination ultracapacitor and battery for micro-hybrids

Opportunities

• Battery has poor cold temperature performance.

• Ultracapacitor has stable performance over temperature.

Also,• Ultracapacitor voltage

window widens at cold temperature delivering higher energy.

• E=1/2*C*V2

Ultracapacitor Potential and Relative Energy(versus Temperature)

01234567

-40 -20 0 20 40 60 80

Temperature (C)

Pot

entia

l (V)

, Rel

E

nerg

y (J

)

+60%

Restivity of Electrolyte of Battery/Ultracapacitor vs. Temperature

0.00

1.00

2.00

3.00

4.005.00

6.00

7.00

8.00

9.00

-40 -20 0 20 40 60 80

Temperature (C)

Rel

ativ

e R

esis

tivity - Battery- Ultracap

- Energy- Voltage

Opportunities

• Studies performed by JME on ultracapacitor and lithium-ion energy storage identified 10s asthe time below which the ultracapacitor is more efficient in energy cycling than the lithium-ion battery.

1

10

100

1000

1 10 100 1000 10000Charging time (s)

Spec

ific

Ener

gy (k

J/kg

)

capacitor

battery

captured

stored

1

10

100

1000

1 10 100 1000 10000Charging time (s)

Spec

ific

Ener

gy (k

J/kg

)

capacitor

battery

captured

stored

Graphic courtesy: J.R. Miller, A.D. Klementov, "Electrochemical Capacitor Performance Compared with the Performance of Advanced Lithium Ion Batteries, Proc. 17th International Seminar on Double Layer Capacitors and Hybrid Energy Storage Devices,” Deerfield Beach, Florida, (Dec. 10-12, 2007).

Graphic compares 12Ah lithium-ion pack vs. 3000F, 2.7V ultracapacitorpack in ability to capture regen energy in an HEV then discharge it. At 100s the lithium will capture 5x more energy than the ultracap but at 10s both capture the same energy only the capacitor discharges 95% of this energy whereas the lithium-ion can only discharge 50%. Therefore, for 10s power the ultracapacitor is 2x as effective as the lithium-ion. Hence, ultracapacitor applicability extends up to 20s versus lithium-ion.

Opportunities

Cycle life of VRLA (alone, active combination)

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

0.00 0.20 0.40 0.60 0.80 1.00 1.20 1.40 1.60 1.80 2.00 2.20 2.40 2.60 2.80

# cycles (pu)

Cap

acity

fact

or

VRLAVRLA+UC

• There are many investigations in progress, and demonstrations that have been completed, that show the improved battery life when using the active combination.

• The example case here is for lead-acid battery with ultracapacitor in active combination (case for lithium-ion is similar, but somewhat less multiplier)

• Cycle life of battery only = 1pu (deep cycles)• Cycle life of active combination = 1.3pu

Opportunities• Power electronic converter facilitates the active combination of capacitor and battery fordecoupled power and energy

• Power electronics is viewed as facilitating next generation energy and power optimized ESS.

Experimental high performance carbon-carbon ultracap 48V module for system level integration

Opportunities

•• Two possibilities:Two possibilities:•• Buffer the battery, orBuffer the battery, or•• As high power interface and energy management of the As high power interface and energy management of the ultracapacitorultracapacitor, , •• Even use a pair of batteries.Even use a pair of batteries.

Source: A. Goodzari, US Hybrid presentation to DOE 2008. Demonstrated that active combination improves overall ESS efficiency by 18% for same $’s.

Fixed dc link converter on ultracapacitor• Overlays existing system implementations• Single point converter failure is not critical• Minimal size ultracapacitor delivers maximum benefitFloating dc link converter on battery• 100% of propulsion steady state power passes thru converter• A single point converter failure cannot be tolerated• Ultracapacitor must be oversized to deliver function.

Opportunities• Combination technologies enable ESS’s for optimized power and energy decoupling.

AM1.

I [A]

-192.00

284.00

0

200.00

0 655.00250.00 500.00t

Load_Profile_P..

AM1... AM

2.I [

A]

Id.I

[A]

-218.0

232.0

0

0 199.0100.0t

Battery and Ul tracapaci tor Cu

AM2.I [A Id.I [A]

Load power profile applied to combination Battery (red) and ultracap (blue) currents for this power

Conclusions

Load power profile applied to combination Battery (red) and ultracap (blue) currents for this power

• Hybrid Vehicles and in particular Plug in HEV are viable intermediate solutions for the existing challenges.

• Ultimate Commercial success of HEV depends on development of high grade Performance electromechanical energy converters and vehicle control systems.

• Long term Energy challenge remains an open problem.

• Texas and in particular UTD should play an effective role in this area.